The present invention relates to vehicle transmissions, especially for heavy, on- and off-road vehicles, and more particularly to dual- and multi-clutch transmissions with a reversing unit that produces several reverse ratios.
Dual clutch transmissions are a cross-breed between conventional stepped transmissions with power interruption at gear shifts and planetary power shifting transmissions, with continuous power transfer through the transmission. In principle, a dual clutch transmission has two input shafts, each connectable to a friction clutch and to the output of the engine. Functionally, this is equivalent to having two conventional transmissions in parallel, i.e., two parallel sub-transmissions, and using one at a time for power transfer. The sub-transmission that is not used, idling, for the irr being, can have a gear engaged and prepared for a subsequent shift. This shift is carried out by simultaneously disengaging the friction clutch of the previously used sub-transmission and engaging the friction clutch of the previously idling sub-transmission.
When properly designed, dual clutch transmissions have the potential of providing power shifts at a reasonable production cost and low power losses. This is due to the fact that the rotating parts, i.e., gearwheels, shafts and tooth clutches, are similar to those in conventional stepped transmissions. This, furthermore, enables the use of the same production equipment.
Some dual clutch transmissions have two separate countershafts, one connected to each input shaft. One example is found in U.S. Pat. No. 5,150,628. The double countershafts make the transmission considerably wider than a conventional stepped transmission. That may lead to difficulties in installing the transmission into the vehicle.
Other dual clutch transmissions are designed such that there is only one countershaft, e.g., as in DE923402 and DE3131156A1. On this countershaft there are loose gearwheels arranged that can be rotationally connected to each other and to the countershaft by means of mechanical tooth clutches. The result is a very compact dual clutch transmission, which enables a power shifting and that is not wider than a corresponding conventional stepped transmission. In these transmissions, there are only two reverse gears though, which is insufficient for heavy severe-duty on- and off road vehicles, such as wheel loaders and articulated haulers. These vehicles require a handful of reverse gears in order to produce both very high tractive force at low vehicle speeds and being able to drive at relatively high speed.
Dual-clutch transmission concepts in a so-called winding structure have been presented, e.g. in DE10339758A1. Therein, the power is led via four gear meshes in at least one gear, and several gearwheels are used for more than one gear. However, this will give just one or two additional reverse gears. Such concepts are hence less suited to heavy on- and off road vehicles.
U.S. Pat. No. 6,958,028B2 shows dual clutch transmission concepts with a special power path for reverse gears between the main transmission and range section. This will result in several selectable reverse gears with appropriate speed ratio steps in between. Typically, the number of reverse gears is half that of forward gears, e.g., four reverse gears and eight forward gears. This is probably sufficient for heavy on- and off road vehicles. However, these designs are bulky and expensive, having two parallel countershafts and a large number of gearwheels.
Hence, there is thus a need for an improved dual-clutch transmission removing the above mentioned disadvantages.
It is desirable to provide a dual-clutch transmission, for heavy duty on- and off road vehicles, which enables high power transfer to the driven wheels during all shifts between consecutive gears, can provide reverse gears for high tractive force to high vehicle speed, is cost-effective and simple to produce, has low power losses and can be easily installed in a vehicle.
According to an aspect of the invention, a multi-clutch transmission, for a heavy duty motor vehicle with at least one prime mover, such as wheel loaders and/or articulated haulers is provided with a first and a second input frictional clutch, input means for establishing a driving connection of said prime mover and said first and second frictional clutches, and a main transmission. By engaging said first input frictional clutch is a first input shaft driven and by engaging said second input frictional clutch is a second input shaft driven.
Said main transmission having a first and a second rotational axis about which a main shaft and a countershaft is arranged respectively, an output shaft and connection means for establishing a driving connection between said main shaft and said output shaft, and at least two input shafts, which are connected to said first and second input frictional clutch, and a reverse shaft provided with a first reverse gear wheel. A reverse gear is achieved by transferring power over the reverse shaft to said output shaft.
Said first and second input frictional clutch is in conventional manner adapted to be in driving connection with said main shaft and said countershaft respectively. Said main transmission is provided with at least four forward speed ratios, between which sequential power shifts can be carried out.
Two of said forward speed ratios thereby transfers power through the first input frictional clutch, and two transfer power through the second input frictional clutch. Normally, the number of forward speed ratios is increased in pairs (one forwards speed ratios per input clutch), wherein the inventive transmission also is suitable for another number of forward speed ratios. An uneven number of forward speed ratios is also imaginable, however not preferred.
As known in the art, a multi-clutch transmission comprises a plurality of gear wheels and clutches arranged upon the main shaft and the countershaft. The different gears of the multi-clutch transmission are thereby achieved in conventional manner, through selective engagement of said clutches.
The inventive multi-clutch transmission is characterised in that it is provided with one gear wheel in said main transmission, which one gear wheel transfers power in all reverse speed ratios and in at least two forward speed ratios, such that shifts between at least four sequential reverse speed ratios can be carried out with a continuous power transfer between said input means and said output shaft.
The inventive multi-clutch transmission thereby provides a plurality of continuous shiftable reverse speed ratios, in the same time as the transmission is compact, due to that the one gear wheel is used in all reverse speed ratios and in at least two forward speed ratios. In the inventive multi-clutch transmission it is possible to have the same number of reverse gears as forward gears, and wherein power shifting between consecutive forward and reverse gears is possible. Because the reverse speeds are provided with a corresponding ratio difference between the speed ratios, the transmission provides reverse gears for high tractive force as well as for high vehicle speeds. The transmission further enables a high power transfer to the driven wheels during all shifts between consecutive gears in both forward and reverse. The transmission is further cost-effective and simple to produce due to its simple construction with only one main shaft, one countershaft, one reverse shaft, and the one gear wheel transferring power in at least two forward gears and all reverse gears. Further due to this inventive design, the transmission can be fitted and easily installed in the limited space available in the vehicles.
The reverse shaft is provided and arranged about a third rotational axis, which is parallel and adjacent to said main first and second rotational axis. Said reverse gear wheel is arranged upon said reverse shaft such that it meshes with said one gear wheel.
Said one gear wheel is preferably arranged upon said counter shaft and is meshing with a gear wheel upon said main shaft and said first reverse gear wheel upon said reverse shaft.
Said one gear wheel is further a loose gear wheel and rotatable arranged upon said countershaft.
A second loose gear wheel is provided upon the countershaft and wherein said one gear wheel and said second loose gear wheel can be engaged with each other through a first gear wheel clutch, such that said second loose gear wheel and said one gear wheel is rotationally fixed to each other. In an engaged state the one gear wheel and the second loose gear wheel acts as a shaft coaxial arranged to the countershaft and which can be rotated independently from the countershaft.
Said reverse shaft is provided with a second reverse gear wheel, which is able to transfer power to a third reverse gear wheel upon said output shaft of said main transmission. By transferring power to said output shaft over said first and second reverse gear wheel upon the reverse shaft, the direction of rotation of the output shaft is opposite to the direction of rotation of the input means of the transmission.
In a preferred embodiment of the inventive multi-clutch transmission, said one gear wheel transfers power in only one gear plane perpendicular to said first and second axis in all reverse speed ratios and in the at least two forward gear ratios. The inventive multi-clutch transmission is thereby held compact.
It is also preferred that the one gear wheel is rotatably arranged upon said countershaft. With this configuration the number of on bearings arranged gear wheels are minimised.
The main shaft of the inventive transmission is preferably suspended in a pilot bearing upon said output shaft.
In order to achieve the double number of gears, it is possible to provide the inventive transmission with a range section. The output shaft is thereby connected to a range section where at least two alternating torque paths having different speed ratios can be established by selective engagement and disengagement of at least one clutch.
The inventive transmission enables plurality of reverse speed ratios in a compact multi-clutch transmission.